The Mechanism Driving a HAB-Induced SST Warming Anomaly: A Case Study in the Beibu Gulf

Abstract

Water temperature is one of the most important factors that affect the occurrence of harmful algal blooms (HABs). Characteristics of sea surface temperature (SST) variability related to a Noctiluca scintillans bloom were analyzed with Himawari-8 data in the Beibu Gulf during mid-February 2021. An SST warming anomaly was found around the bloom area from 10:00 to 19:00 local time, with a peak temperature of 24.3 °C at 15:00, which was 2.9 °C higher than the surrounding normal sea water. The possible formation mechanism of the HAB-induced SST anomaly was studied in this work by integrating meteorological, ocean dynamics, and ecological processes. During the HAB event, the sea surface was covered by biological mucilage. A model that considered the net heat flux, heat capacity, density of seawater, and temperature variation was established to estimate the thickness changes (ΔH) in the marine heating layer during the HAB event. The model results show that the heating layer thickness of the HAB area (ΔH between 0.76 m and 0.91 m) was smaller than that of the non-HAB area (ΔH > 1.19 m). The SST anomaly in this study might be caused by a thinner and warmer marine heating layer that is related to the biological mucilage on the surface of the HAB area.